Acoustical device



July l, 1930. J@ KULLMAN 1,769,438"

ACOUSTICAL DEVICE Filed June 14, 1929 2 Sheets-Sheet 2 Illlllllllllllllllllllllllll .111111 f IN V EN TOR.' I Jca fv//man wlfw A TTORNEYS.

Patented July 1', 1930 PATENT OFFICE JACOB KULLMAN, 0F HILLVSBOROUGH, CALIFORNIA ACOUSTICAL DEVICE Application led .Tune 14,

This invention relates generally to acoustical devices in which mechanical vibrations are translated into sound. It hasparticular application to the construction of devices excited With electrical current variations of voice frequencies, such as loud speakers.

It is a general object of the present invention to devise a loud speaker or equivalent device which Will give substantially faithful reproduction of voice or musical frequencies.

It is a further object of thisinvention to devise a novel form of sound baille for use in combination with an acoustical device, such as a loud speaker reproducing unit, which Will increase the quality of reproduction and will make the tones more pleasing.

Further objects of the invention Will appear from the following description in Which I have set forth the preferred embodiment of my invention. It is to be understood that the appended claims are to be accorded a range of equivalents consistent with the state of the prior art.

Referring to the drawing:

i Figure 1 is a side elevational view in cross section, illustrating a device constructed in accordance with my invention.

- Fig. 2 is a front view of a portion of the device shown in Fig. 1.

Fig. 3 is a side elevation in cross section, illustrating a modification .of my device.

Fig. 4 is a front elevational View showing a portion of the devise shown in Fig. 3.

In loud speakers which have been used in the past, it has been found desirable to employ baffles in conjunction with sound reproducing units, in order to secure proper rreproduction of the lower tones. For example in a loud speaker of the type utilizing a tympanum or other form of diaphragm vibrated mechani- `cally by a magnetic driving unit, the bale extends outwardly for a substantial distance from the periphery of the tympanum. If the magnetic unit is mounted Within a cabinet, as for example in the cabinet of a radioreceiving set, the front and side Walls of the cabinet form the required baille. Balles which have been used in the past have been constructed of Wood, pressed fibre, or equivalent 19:29.y serial No. 370,814.

material. In developing loud speakers which will give superior quality of reproduction, I have discovered that the tones produced by a iven reproduction unit can be materially in uenced bv utilizing hide in place of Wood or pressed bre for the battle construction. By comparative test I have found that a loud speaker having a hide baffle will reproduce tones over the entire voice frequency range more faithfully and of better quality, the shrill and harsh tones generally reproduced by a loud speaker are minimized, and the general tonal effect is more pleasing.

Referring to the drawing` for one specific form of my invention, in Figs. l and 2 I have shown a conical diaphragm or tympanum 10 in conjunction with a magnetic driving device 11. Devi 11 may be of the dynamic type .in which a coil l2 is secured to the apex of cone v10 and operates Within an annular magnetic gap. A permanent magnetic fieldk can be provided, or device 11 can have a field Winding connected to a suitable source of current. Electrical current variations of voice frequencies, as Lfor example that obtained from the output of a radio receiving set, are impressed upon the coil 12. The inner portion of the cone 10 is shown resiliently supported by means of spring strips 13, While the periphery is resiliently supported by a i flexible edge portion 14. A suitable rigid frame 16, carried by the magnetic device 11, serves as a support for the flexible edge portion 14. The baille which is used in conjunction with tympanum 10, is formed by one or .4

more pieces of hide 17 supportedby a suitable frame. The fra-me in this instance consists of an outer structure 18 serving `as a support for the outer peripheral edge of the hide, andan inner structure 19 which terminates the inner edge of the hide near the outer periphery of the tympanum 10. Frame 18 can be supported in any suitable manner on a cabinet or other mounting for the loud speaker, or if desired, hide 21 and f rmf 1,8 e

can be supported by each other and both carriedrby inner frame 19. The hide is preferably stretched upon the frame with considerable tension. The extent of the baffle from the peripheral edge of the tympanum should be suhicient to insure proper reproduction otl the loiv tones. Since the minimum dimension requirements for acoustical bales of this kind are Well known in the art, this matter need not be explained in detail.

I have Jound that the hides may be cured or uncured, although for strength and ease in manufacture, it is preferably cured. It is also possible to use the hide with or Without the natural hide hair. The hide Without hair has been found to be of marked advantage over baille materials which have been used in the past, although best results have been secured by utilizing hide having its hair l5 upon one surface of the same, as indicated at Q1. The exact manner in which the layer ot hair contributes to the success of my invention is not clear. Probably the hair entraps a layer of cushioniner air in front of 2O the baiile, and the individual hairs in following the movements of the air particles probabi)v exerts a damping action. If the damping action actuallyv occurs, it is not suflicient to cause distortion of the reproduced tones, but reduces the intensity or absorbs the relativel'v high freevuencv shrill tones or noises, which detract from the desired musical tones. In order that the hair upon the hide be most effective`r it is preferablyv faced toward the 30 front of the speaker. or towards that side of the speaker from which the sound is being propagated.

In Figs. 3 and 4 I have illustrated another toi-m ot baille which is in the form of a truncated cone, rather than planar as shown in Figs. 1 and 2. In this case a metal spacing structure Qi connects together the inner and outer frame structures 118. 119 upon which the hide 11T is stretched. IVhen positioned upon the iranie, the form of the hide is such that it continues the conical form of the tympanum 10. Particularlv goed results have been achieved With a baiiie of this form made ot hide, both with respect to the quality of reproduction and to the propagation of the sound Waves in a given direction.

I claiin:

1. An acoustical device comprising a sound translating unit, and a sound baille extending over a substantial area and formed of hide having hair on one side ofthe saine.

2. An acoustical device comprising a tympanum, magnetic means serving to vibrate said tvmpanum to generate sound waves. and a baiile extending from the periphery of the tyinpanum over a substantial area. said baffle being formed of hide having hair upon its forward surface.

In testimony whereof, I have hereunto set my hand.

JACOB KULLMAN. 

